The goal of this multi-site, multi-PI proposal is to gain a mechanistic understanding of the genetic and environmental factors governing the ability of red blood cells (RBCs) to handle oxidative stress. RBC transfusion is the single most common therapeutic intervention for hospitalized patients; however, there is substantial donor-to-donor variability in how RBCs store, circulate, and function post-transfusion. There is similar variability in recipient responses to transfusion, due to the wide range of diseases requiring this life- saving therapy. Our preliminary data using mouse models, linked to and followed by human studies, demonstrate that lipid metabolism, in general, and eicosanoid generation, in particular, predict RBC quality. We also identified a novel enzymatic pathway (i.e., Steap3) responsible for determining RBC storage quality of various mouse strains. Finally, we identified a novel role for diet (both iron and fatty acid consumption) in modifying lipid oxidation in RBC membranes and affecting RBC quality. Together, these findings led to our central hypothesis that oxidant stress, and factors influencing it, is a critical determinant of RBC storage quality. This proposal represents a multi-institutional collaboration of scientists with diverse expertise in transfusion biology, mouse models, human studies, ?omics? approaches, and RBC and lipid biochemistry, aimed to improve our understanding of genetic and environmental determinants of RBC quality. Thus, in Aim #1, we will elucidate donor and recipient genetic and environmental factors by which oxidant stress affects RBC transfusion in mouse models. In Aim #2, we will identify which results in mice are translatable to the human setting and will provide mechanistic details in humans. The effects of elevated oxidant stress in sickle cell disease recipients on the biology of the transfused RBCs will also be directly examined. This proposal is designed to provide dynamic cross-germination between Aims, allowing for iterative and ongoing mechanistic studies, which simultaneously exploit the strengths and mitigate the weaknesses of animal and human studies, respectively. This research will lead to innovative and eminently translatable approaches for improving transfusion therapy and will enhance basic mechanistic understanding of RBC oxidant stress handling.